cardiovascular impairments are the main cause of death in the western world. Cardiovascular problems are often related to or accompanied by stenosis in arteries, increase of arterial stiffness, hypertension, or other vascular changes, be it anatomical or physiological.
Assessment of the vascular system of humans has been subject of more than a century of research and development. Blood pressure measurements using the well-known sphygmomanometer, assessment using ultrasound (including Doppler), various ways of measurement of pressure waves, plethysmography and angiography have been used both clinically and in research.
However, there are one or more problems associated with all of the above known measurement methods. The known measurement methods may be expensive, such as ultrasound assessment and plethysmography, and/or invasive, such as angiography. Further, there may be a need to obtain more information than possible with the known measurement methods. For instance, the measurement methods may only obtain limited information on the vascular tree, such as when using a sphygmomanometer. Further, the known measurement methods may not give information about a part of the vascular system that actually matters.
It may often be important to obtain information about the central, abdominal or big arteries, such as aorta, carotid arteries, iliac arteries with branches, renal arteries, mesenteric arteries, and femoral arteries. Such information may provide an indication of a state of health/disease or may be used for assessment of medication induced changes to the vascular system. For instance, assessment or monitoring of the vascular system may be needed in relation to use of vasodilatory drugs, in assessing vascular disease, including coronary artery disease and diastolic dysfunction, in anesthesiology/intensive care for monitoring cardiac output, diabetes, kidney disease, rheumatoid arthritis, hypercholesterolemia, hyperlipidemia, or exercise monitoring.
The assessment and monitoring of the vascular system may present different problems depending on the particular use of the assessment and monitoring.
A specific area of interest is assessment and monitoring of cardiovascular changes in relation to pregnancies, births, and post-partum changes. There is a great interest in accomplishing early detection of any complications related to a pregnancy.
In particular, the vascularization of the uterus and the placenta of the pregnant woman may provide indications of the cardiovascular risk of the pregnant woman, and also whether the fetus is developing normally. It is possible to measure the blood flow of uterine and umbilical arteries of the pregnant woman using Doppler velocimetry. However, this requires the use of ultrasound scanning equipment, and the measurement needs to be performed by trained medical staff. Hence, the measurement of the blood flow may only be performed on occasion, requiring the pregnant woman to come to a clinic and involving medical staff for performing the measurement, and with the risk of undiscovered cardiovascular deterioration in the meantime.
Typically, monitoring of uterine and umbilical arterial blood flow is only started, when it is detected by other means that the fetus may not be developing normally or when the pregnant woman belongs to a high risk group. Monitoring may thus be used in cases such as: Intra Uterine Growth Restriction (IUGR), twin pregnancy, maternal hypertension, maternal pre-eclampsia, maternal diabetes, placental insufficiency leading to premature birth, miscarry or stillbirth, and women pregnant after In Vitro Fertilization (IVF).
When diagnosed as having a fetus not developing normally or belonging to a high risk group, the pregnant woman may become anxious and worry about the state of the fetus. The woman may therefore frequently ask for examinations to check the state of the fetus, whereby hospital resources are demanded each time an examination is made. Further, the nervous tension felt by the pregnant woman may also act to aggravate the condition, for instance when the pregnant woman suffers from pre-eclampsia or hypertensive disorder. Therefore, any method for allowing the pregnant woman to make an examination at home would be beneficial both in terms of medical resources required and in providing a possibility for the pregnant woman to check the condition of the fetus whenever worries arise.
Also, the sensitivity of uterine artery Doppler velocimetry using ultrasound increases proportionally with early onset of the clinical manifestations of IUGR and pre-eclampsia and with their severity, but the Doppler velocimetry has a low specificity which may lead to expected iatrogenic premature births and unnecessary interventions in the pregnancy contributing to maternal and neonatal morbidity and mortality.
Preeclampsia is one of the leading causes of pregnancy related maternal morbidity and mortality. In addition to the immediate risk, women who recover from preeclampsia are more likely to experience life-threatening cardiovascular disease later in life. The cardiovascular risk in preeclampsia is associated with increased central arterial stiffness and measures of arterial function as pulse wave analysis or pulse wave velocity (as increased carotid or femoral pulse wave velocity) is useful for clinical assessments.
As is evident from the above, it would be desirable to provide an improved method for continuously assessing the cardiovascular status of the pregnant woman and the development of a fetus. In particular, it would be desirable to provide a method that does not require medical staff to perform measurements and which may be performed by the pregnant woman in her home.
WO 2013/079073 discloses a system for monitoring a fetus in a pregnant woman. The system comprises a portable unit that can be worn by the pregnant woman so as to allow monitoring during daily life. The portable unit has a sound sensor to be positioned on the skin of the abdominal area of the pregnant woman so as to detect a vascular sound from the umbilical arteries of the fetus or from the uterine arteries of the pregnant woman. The sound sensor is functionally connected to a processing unit which executes a processing algorithm on the captured vascular sound and extracts a signal parameter accordingly.
The system allows a measurement of vascular sound to be made by means of a sound sensor that may be worn by the pregnant woman during daily life. Hence, the system may reduce the need for the pregnant woman to be examined at a medical clinic and may also reduce anxiety of the pregnant woman as the state of the fetus may be continuously monitored.
Although the technology disclosed in WO 2013/079073 may enable monitoring of a pregnant woman in her home, there is still room for improvement in the analysis of the vascular sound in order to determine a condition of the fetus.